CELLS LINING THE PERITONEAL CAVITY 409 
The omentum 
When the omentum from a rabbit that had been vitally stained 
with trypan blue was spread on a cover-slip, treated lightly with 
silver nitrate and stained with carmine, the large pavement 
cells of the serosa were found to be very characteristically stained. 
They almost always contained a small ring of blue granules in 
one part of the cytoplasm, sometimes this ring was entirely 
regular and smooth in contour and again it was broken or oval 
shaped. These granules appeared in animals which had re- 
ceived only a few doses of blue; when the staining was carried 
further, the cytoplasm in the neighborhood of this first ring-like 
group of granules began to show a few additional granules, and 
finally the perinuclear rosette developed. In an animal in which 
the staining was carried out with the usual amount of dye, six 
to eight doses, the sharply defined area was very characteristic 
and the ring was still present though obscured by the develop- 
ment of some diffuse granules adjacent to it. The perinuclear 
rosette was present in about one-half to one-third of the cells, 
but was usually quite irregular. Perhaps the most interesting 
and characteristic finding was that, in the majority of the cells, 
the ring and its subsequently attached granules were opposite 
the long axis of the oval nucleus (fig. 5). Most of the mesothelial 
cells covering the omentum were rather elongated, and with the 
patches of dye-granules located in one end they presented a very 
characteristic appearance. With longer exposures to blue, the 
granules gradually extended throughout the end of the cell and 
a few appeared irregularly elsewhere in the cytoplasm, increasing 
the sharpness of the perinuclear rosette, and sometimes appearing 
over or under the nucleus. Occasionally there were two sharp 
areas of localization in a single cell, but this was not common in 
the normal cells except in those where there were two nuclei; 
in such instances the arrangement was usually of one or two 
types. In many cells the dye-granules were arranged about 
each nucleus as though the cell might be in process of division, 
suggesting that each group of granules eventually would be 
entirely characteristic of an individual cell. In others there 
